Water-intensive processes, such as papermaking and cooling water processes, are offering a fertile environment for microbiological growth. Therefore biocidal treatments are often necessary in various water-containing processes. The target of biocidal treatments in industry is not usually a complete sterilization, but a contribution for finding a stable, dynamic balance of microbial growth on an acceptable and cost-efficient level. The prior art relates to wide variety of biocides in different kind of applications within water-intensive industries, paper industry being one of the biggest. Within that area it is estimated that a part of the applications are currently using technologies that could be replaced if more effective biofilm-control technology based on targeted biocides could be found.
A biofilm is an aggregate of microorganisms in which cells adhere to each other on a surface. These adherent cells are frequently embedded within a self-produced matrix of extracellular polymeric substance (EPS). Biofilm EPS, which is also referred to as slime, is a polymeric conglomeration generally composed of extracellular DNA, proteins, and polysaccharides. Biofilms may form on living or non-living surfaces and can be prevalent in natural, industrial and hospital settings. The microbial cells growing in a biofilm are physiologically distinct from planktonic cells of the same organism, which, by contrast, are single-cells that may float or swim in a liquid medium.
Formation of a biofilm begins with the attachment of free-floating microorganisms to a surface. These first colonists adhere to the surface initially through weak, reversible adhesion via van der Waals forces. If the colonists are not immediately separated from the surface, they can anchor themselves more permanently using cell adhesion structures such as pili. Some species are not able to attach to a surface on their own but are often able to anchor themselves to the EPS matrix or directly to earlier colonists. It is during this colonization that the cells are able to communicate via quorum sensing using such signals as AHL compounds. Once colonization has begun, the biofilm grows through a combination of cell division and recruitment. The final stage of biofilm formation is known as development, and is the stage in which the biofilm is established and may only change in shape and size. The development of a biofilm may allow for an aggregate cell colony (or colonies) to be increasingly antibiotic resistant.
Biofilms contribute in many problems in aqueous industrial systems, such as recirculating systems, e.g. paper machines or cooling systems. The build-up of surface contaminants such as biofilms can cause problems such as poor heat transfer, high energy consumption, corrosion, increased maintenance expenditures, shortened system life, high operating costs, unscheduled down time of the equipment etc.
A biocide is an antimicrobial chemical substance which can deter, render harm-less, or exert a controlling effect on any harmful organism. Biocides are commonly used in medicine, agriculture, forestry, and industry. A biocide may be further classified as a germicide, an antibiotic, an antibacterial, an antiviral, an antifungal, an antiprotozoal or an antiparasite.
Most of the current biocides have been developed for the control of planktonic bacteria. At the generally used low concentrations such biocides are not very effective against biofilms. The sheath or matrix formed by EPS-producing microorganisms makes them tolerate higher dosages of most of the common biocides. Using high doses of biocides may cause other problems, such as corrosion of the equipment. Also, because biocides are intended to kill living organisms, increasing dosages of biocidal products increases risks for human health and welfare.
There is a need for better biocides which can be used against biofilms on surfaces. They should be able to be targeted to the biofilms and advantageously also be able to penetrate the biofilm and kill the biofilm organisms. Such biocides should be effective also at low doses.